<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
  <html xmlns="http://www.w3.org/1999/xhtml">
    <head>
       <meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
       <title>??</title>
       <style type="text/css">
          *{margin:0;padding:0;}

           .layer2{width:99%;}
  
             .layer2-1{width:33%; height:230px; background:red;text-align:center;float:left;}  
             .layer2-2{width:33%; height:230px; background:orange;text-align:center;float:left;} 
            .layer2-4{width:33%; height:230px; background:pink;text-align:center;float:left;} 
             .layer2-3{clear:both;}   
           .layer3{width:99%;}
             .layer3-1{width:99%; height:150px; background:green;text-align:center;float:left;}
           .layer4{width:99%;}
             .layer4-1{width:100%; height:150px; background:orange;text-align:center;float:left;}


       </style>
    </head>
    <body>

       <div class="layer2">
            <div class="layer2-1"></div>
            <div class="layer2-2"></div>
            <div class="layer2-4"></div>
            <div class="layer2-3"></div>
       </div>  
       <div class="layer3">
            <div class="layer3-1"></div>
       <div class="layer4">  
            <div class="layer4-1"></div>


    </body>
 </html>